AY Honors/Porifera and Cnidaria/Answer Key

1. Why are sponges considered animals?

The Porifera, or sponges, are multicellular filter-feeders, drawing particles out of the water column and ingesting these for nutrients. The general action of sponges, then, helps categorize them as animals, rather than as plants. However, some scientists argue that Sponges may belong in their own kingdom, due to some unique characteristics. These include the ability of many sponges to group from single cells, forming back into the full set of differentiated cells of a sponge, and the fact that isolated sponge cells cannot live alone for long (unlike colonial animals, like bryozoans, which are cooperative cells, but not necessary to one an other).

2. Why are they considered filters?

Sponges have pores (called Ostia) which allow water to pass into their structure, drawn by the action of flagellum on specialized cells (Chanocytes). These Chanocytes are ringed with smaller hair-like structures that filter particles out of the water column, moving these particles into the sponge. Specialized cells (Amebocytes) move within a jelly-like matrix between the outer and inner “skin” of the sponge, and carry out digestion. These cells can also replace other cells, changing form and function as needed. The water that was drawn in the Ostia flows back out another pore, the Osculum.

3. Name at least two characteristics of sponges.

Sponges are multicellular animals with an outer and inner membrane (the Ectoderm and Endoderm respectively), with a non-cellular jelly-like matrix between these cellular layers. Sponges have specialized Chanocytes, cells with a flagellum to create a current to draw water over special hair-like projections in a ring around the flagellum. Sponges gain structural strength from spicules, which in some form a type of skeleton. Spicules can be made of protein fibers, silica (glass) or calcium carbonate. Sponges are sessile, they do not move (though certain embryonic stages are capable of movement). Sponges do not necessarily have any particular symmetry to their body form.